Abstract: Ovarian aging is the major underlying cause of reproductive senescence and its associated morbidities, which affect a significant proportion of the female population (Li et al, Human Reproduction, 2013). Cancer therapy induces acceleration of ovarian aging and could potentially involve 1% of the female population over their reproductive life span. My mentor's laboratory discovered that gonadotoxic chemotherapeutics result in primordial follicle death primarily by causing DNA double strand breaks (DSBs) in oocytes. My mentor's laboratory also found that this insult triggers an ATM-mediated DNA DSB repair response (Soleimani et al, Aging, 2011), which may enable some primordial follicles to survive this intense genotoxic stress. Furthermore, our laboratory found that DNA DSB repair response is critical in the way oocytes mitigate other genotoxic insults that may be causing aging, and that women who are deficient in DNA DSB repair, specifically BRCA1- mutation carriers, may be prone to prematurely depleting their ovarian reserve (Titus et al, Science Translation, 2013). In addition, our laboratory showed that Sphingosine-1-Phosphate (S1P), a naturally occurring ceramide death-pathway inhibitor, reduces chemotherapy-induced primordial follicle death in human ovarian xenografts (Li et al, Human Reproduction, 2013). Stemming from these discoveries, we hypothesize that pharmacological manipulation of DNA DSB repair mechanisms may temper ovarian aging caused by genotoxic stress. Our overarching aim is to uncover the mechanisms by which S1P protects primordial follicles against genotoxic death and to determine whether S1P's protective effect is applicable to reproductive aging in general. Our specific aims are: 1. To determine whether S1P prevents chemotherapy-induced ovarian aging by enhancing oocyte DNA DSB repair in vitro in mice; 2. To translate the findings from aim 1 to human and to determine if S1P enhances DNA repair in human primordial follicle oocytes in vivo; 3. To determine whether S1P can slow down reproductive aging in vivo in mice. To achieve these aims we will utilize numerous translational approaches that have been previously successful in our laboratory, including but not limited to single cell real time PCR as well as microarray strategies, gene interference, coupled with human ovarian xenografting and laser capture.